Frodo will be reading "There and Back Again," so we are seeing the events of The Hobbit as written by Bilbo.

So given this format, how are they going to make the White Council and Dol Guldur scenes work, given that Bilbo wasn't present for those events? How would he have them recorded? How would he know what all was said? Or how they drove the Necromancer from the tower. I doubt Gandalf would have told him every single detail regarding the Council and their seige on Dol Guldur. To my knowledge, all Gandalf told Bilbo of the whole affair was that he went away to deal with the Necromancer - without getting into too many specific details. I'll have to double check.

If the events of The Hobbit were being told in real-time, and not strictly through Bilbo's eyes, this wouldn't be an issue.